A miniature confocal optical system that is used along the channel of an endoscope is described in Japanese Laid Open Patent Applications H9-230248 and H3-87804. A prior art schematic diagram showing the principle components used with a confocal optical system that may be inserted in a channel of an endoscope for viewing an object of interest is shown in FIG. 8.
Referring to FIG. 8, light from a light source 51 enters a four-terminal optical coupler 52, which leads the light to a miniature confocal optical system 54. The miniature confocal optical system 54 focuses the light onto an object. Light reflected by the object is detected at an optical detection unit 53 after it has been propagated through the miniature confocal optical system 54 and the four-terminal optical coupler 52. The detected light is processed at a processing unit 55 in order to image the object The miniature confocal optical system 54 is inserted in a channel of an endoscope in order to observe and diagnose cells inside a human body. As is shown in FIG. 9, the miniature confocal optical system 54 is of the side-view type, in which the viewing direction is orthogonal to the direction of insertion of the miniature confocal optical system 54.
Conventional endoscopes are generally of the straight-view type, in which the viewing direction is aligned with the direction of insertion of the endoscope. When a side-view type miniature confocal optical system is inserted in the channel of a straight-view type endoscope, inconsistency in the viewing directions of the endoscope""s objective lens versus the miniature confocal optical system may give rise to a problem in that the observation range of the miniature confocal optical system cannot be determined by viewing through the objective lens of the endoscope.
To solve this problem, a straight-view type miniature confocal optical system may be used, as shown in FIG. 7, with a straight-view type endoscope. This facilitates determining the location and range of observation of the miniature confocal optical system by viewing through the objective lens of the endoscope. Thus, locating the view of the miniature confocal optical system on an object of interest is facilitated. Therefore, a straight-view type, miniature confocal optical system is more easily used with a straight-view type endoscope.
Objects inside a human body, particularly cells, reflect light rather poorly. Thus, the optical signals of interest tend to be very weak. On the other hand optical noise (i.e., light which reflects on a lens or other surface within the optical system and directly returns to the optical fiber without reaching the object), is rather strong as compared to the optical signals of interest. Therefore, it is critical to suppress the optical noise as much as possible.
The present invention relates to a confocal optical system, especially to a miniature confocal optical system that may be used along the channel of an endoscope. A first object of the present invention is to provide a miniature confocal optical system which enables the observation of poorly reflective objects with a high signal-to-noise ratio S/N. A second object of the invention is to provide a miniature confocal optical system of the straight-view type having a high S/N which can be inserted into the channel of an endoscope.